1. Field of the Invention
This invention relates to a power line communication MODEM for transferring data from an information processing unit such as a personal computer through a power line.
2. Description of the Related Art
A power line communication MODEM (abbreviated as “PLC MODEM”) is known as means that makes it possible to use a power line such as a distribution line for supplying power from a substation to each home and interior wiring extended in each home as a communication line. The PLC MODEM converts digital data from an information processing unit such as a personal computer to analog line data, overlaps the analog line data with a power line of a commercial power source, or converts the analog line data inputted through the power line to digital signals and transfers them to the information processing unit. Therefore, the PLC MODEM can constitute a communication network among information processing units.
FIG. 3 shows a PLC MODEM according to the prior art and a connection diagram when a communication network is constituted by use of the PLC MODEM. This PLC MODEM 40 includes a power source unit (AC adaptor) 41 having an attachment plug 41a with an AC cord fitted thereto, a MODEM main body unit 42 and a DC cord 43 for connecting the power source unit 41 to the MODEM main body unit 42. The power source unit 41 has a rectification circuit (not shown) for converting a commercial AC power source to a DC power source, and a DC voltage is supplied to the MODEM main body unit 42 through the cord 43.
The MODEM main body unit 42 has a rectangular parallelepiped shape, accommodates therein a MODEM circuit (not shown) and includes a connector of a USB standard (called “USB connector”) 42a fitted to one of its side surfaces. The MODEM circuit converts the digital data inputted from the USB connector 42a to the analog line data and overlaps the analog line data with the DC voltage of the DC cord 43. The analog line data is further overlapped with the AC power source in the power source unit 41.
On the other hand, the DC power source is supplied from a power source unit (AC adaptor) 45 to an information processing unit 44 such as a notebook type personal computer. An AC cord 45a having an attachment plug and a DC cord 45b having a plug are connected to the power source unit 45. A USB connector (not shown) is fitted to the information processing unit 44, too. The USB connector 42a of the MODEM main body unit 42 and the USB connector of the information processing unit 44 are connected to each other through a USB cable 46.
In the construction described above, when the digital data is inputted from the information processing unit 44 to the MODEM main body unit 42, the MODEM circuit converts the digital data to the analog line data and overlaps the analog line data with the DC cord 43 for supplying the DC voltage. The analog line data is sent to the interior wiring through the attachment plug 41a. Therefore, data communication can be mutually made with other information processing unit inside the same home through the interior wiring. Mutual communication can also be made with other home through the distribution line.
The PLC MODEM and the information processing unit must always be used as a pair. Therefore, when no more spare plug sockets are available, a plug socket must be secured for the information processing unit used together with that for the PLC modem. Alternatively, another plug socket must be provided for branching the plug socket.
The information processing unit is connected to the PLC MODEM and at the same time, must be connected per se to the power source unit. Therefore, mutual connection gets complicated.